The aim of this study was to investigate the effects of ALC treatment on cognitive functions in patients with severe hepatic encephalopathy. This was a randomized, double-blind, placebo-controlled study. 61 patients with severe hepatic encephalopathy were recruited to the study. The 2 groups received either 2 g ALC twice a day (n = 30) or placebo (n = 30) for 90 days. Clinical and laboratory assessment, psychometric tests and automated electroencephalogram (EEG) analysis were performed for all patients. At the end of the study period, between the 2 groups we observed a significant difference in Everyday Memory Questionnaire -23.9 vs 4.4 (p < 0.001), Logical Memory (Paragraph recall) test 22.3 vs 0.7 (p < 0.001), Trail Making Test A -7.5 vs -2.6 (p < 0.001), Trail Making Test B -10.5 vs -3.1 (p < 0.001), Controlled Oral Word Association Test 4.2 vs 0.5 (p < 0.001), Hooper test 2.6 vs 0.1 (p < 0.05), Judgement of line orientation 2.8 vs 0.3 (p < 0.001), Digit Cancellation time -24.5 vs -2.4 (p < 0.001), NH₄⁺ 30.5 vs 13.5 (p < 0.001), prothrombin time 2 vs 2.4 (p < 0.05), alanine transaminase -10.7 vs -13.6 (p < 0.001). 88% of patients treated with ALC vs 72% of patients treated with placebo showed a significant improvement in EEG. The improvement of cognitive deficits, the reduction of ammonia, and the modification of EEG in patients treated with ALC suggest that ALC could represent a new tool in the treatment of severe hepatic encephalopathy.